According to an analysis by FiveThirtyEight founder Nate Silver, Philly is the fourth-most segregated city out of the 100 biggest cities in the country. To determine how divided a city is, he first looked at something called the “citywide diversity index”:

It’s defined as the answer to this question: For an average resident in the city, what percent of the people belong to a different racial group?

The lowest possible citywide diversity index is 0 percent, which is what you get if everyone is the same race. The highest possible one is 80 percent. Why not 100 percent? Because the Brown data only includes five racial groups. Even if the population is divided exactly evenly between these groups, you’ll still have 20 percent of the people belong to the same race as you.

Philadelphia’s citywide diversity index is 65.6 percent, which isn’t that far off from the most diverse areas in the country. At 75.5 percent, Jersey City, N.J. has the highest citywide diversity index in the country. Chicago, which is also up there, has an index of 70.3 percent.

But Silver also looked at something called the “neighborhood diversity index,” which asks, “For an average resident in the city, what percent of the people in her neighborhood belong to a different racial group?” At the neighborhood level, Philadelphia isn’t diverse at all. Its neighborhood citywide index is just 38.6 percent. Silver then looked at the relationship between the citywide diversity index and the neighborhood diversity index to determine a city’s integration-segregation index. Here, Philadelphia gets a score of negative 12.6 percent.

Philly is far from alone in being both diverse and segregated. The headline of Silver’s analysis is “The Most Diverse Cities Are Often the Most Segregated.”